下列花的各部分结构中，能形成种子的是（ ）
A．胚珠
B．房
C．受精卵
D．胚
当一朵花开发之后必须完成传粉与受精，才能结出果实和种子，传粉是指雄蕊的花粉落到雌蕊的柱头上的过程．受精是指精子和卵细胞结合成受精卵的过程．一般当花完成传粉与受精后只有子房进一步发育为果实，子房壁发育成果皮，胚珠发育成种子，珠被发育成种皮，受精卵发育成胚，受精极核发育成胚乳，可见A符合题意．
故选A
Directions: There are 10 blanks in the following passage. For each numbered blank, there are 4 choices marked A, B, C and D.
| The United States is well-known for its network of major highways designed to help a driver get from one place to another in the shortest possible time. (51) these wide modern roads are generally smooth and well maintained, with (52) sharp curves and many straight sections, a direct route is not always the most (53) one. Large highways often pass by scenic areas and interesting small towns. Furthermore, these highways generally (54) large urban centers which means that they become crowded with heavy traffic during rush hours, (55) the "fast, direct" way becomes a very slow route. However, there is almost always another route to take (56) you are not in a hurry. Not far from the (57) new "super highways", there are often older, less heavily traveled roads which go through the countryside. (58) of these are good two-lane roads; others are uneven roads curling through the country. These secondary routes may go up steep slopes, along high cliffs, or down frightening hillsides to towns (59) in deep valleys. Through these less direct routes, longer and slower, they generally go to place where the air is clean and the scenery is beautiful, and the driver may have a (60) to get a fresh, clean view of the world. |
A．little
B．few
C．much
D．many